This exception indicates a problem with an XPathExpression, such as an invalid prefix.

public class XPathException : SystemException {
// Public Constructors
   public XPathException(string message, Exception innerException);
// Protected Constructors
   protected XPathException(System.Runtime.Serialization.SerializationInfo info,
       System.Runtime.Serialization.StreamingContext context);
// Public Instance Properties
   public override string Message{get; } 
// overrides Exception
// Public Instance Methods
   public override void GetObjectData(System.Runtime.Serialization.SerializationInfo info,
        System.Runtime.Serialization.StreamingContext context)
// overrides Exception
}

Hierarchy

System.Object System.Exception(System.Runtime.Serialization.ISerializable) System.SystemException XPathException